The present invention relates to radiant electric heaters, such as for use in cooking appliances and more especially for use in cooking appliances having glass-ceramic cooking surfaces.
It is well known to provide a radiant electric heater for use in a cooking appliance beneath a glass-ceramic cooking surface and in which at least two concentrically-arranged heating elements, separated by a dividing wall of thermal insulation material, are supported on or adjacent to a base of thermal insulation material, such as microporous thermal and electrical insulation material. An outer heating zone and an inner heating zone are thereby provided, the inner heating zone having one or more heating elements which are generally arranged to be energisable independently of the heating element or elements of the outer heating zone.
A peripheral wall of thermal insulation material is generally arranged around the edge of the heater and a rod-like temperature-responsive device extends from a periphery of the heater across the heater to a position at least partly across the inner heating zone.
In order to meet a requirement that the temperature-responsive device should be responsive substantially only to heat from the inner heating zone, even when both inner and outer heating zones are energised, it is known to provide a tunnel of thermal insulation material supported on the base and covering the rod-like temperature-responsive device between the peripheral wall and the dividing wall in the outer heating zone. The heating element in the outer heating zone is arranged to stop short of the tunnel at either side thereof and hence does not intrude into the tunnel. The temperature-responsive device is thus thermally isolated from the heating element in the outer heating zone.
It is further known to provide one or more end portions of the heating element of the inner heating zone extending into the tunnel through an aperture in the dividing wall. Such one or more end portions of the heating element are led through the tunnel and out to terminals of a terminal block, located at the edge of the heater, for electrically connecting the element of the inner heating zone to a power supply. The terminal block is generally located near the end of the temperature-responsive device at the edge of the heater.
The heating element of the outer heating zone also has end portions which are electrically connected to terminals in the terminal block and it is usual to provide a common terminal to which is electrically connected an end portion of the heating element of the outer heating zone and also an end portion of the heating element of the inner heating zone. Two further terminals are usually provided, one connected to another end portion of the heating element of the inner heating zone and the other connected to another end portion of the heating element of the outer heating zone.
Such an arrangement has hitherto placed a restriction on the possible permutations available for making external connections to the terminal block. The common terminal was generally restricted to a position intermediate the other two terminals because if it was required, for example, to provide the common terminal as one of the other terminals, particularly a terminal nearer the temperature-responsive device, the other end portion of the heating element of the outer heating zone leading thereto would provide a barrier against connection of the other end portion of the heating element of the inner heating zone to one of the remaining terminals.
It is an object of the present invention to overcome or minimise this problem.
According to the present invention there is provided a radiant electric heater comprising: a base of thermal insulation material having supported relative (thereon or adjacent) thereto at least two concentrically-arranged heating elements separated by a dividing wall of thermal insulation material to form an outer heating zone and an inner heating zone, the heater having a peripheral wall of thermal insulation material; a tunnel formed of thermal insulation material extending between the peripheral wall and the dividing wall across the outer heating zone; a rod-like temperature-responsive device extending from a periphery of the heater through the tunnel and at least partly across the inner heating zone, through an aperture provided in the dividing wall; one or more end portions of one or more heating elements of the inner heating zone extending along the tunnel; a terminal block located at the periphery of the heater, the one or more end portions of the one or more heating elements of the inner heating zone and one or more end portions of one or more heating elements of the outer heating zone being electrically connected to terminals provided in the terminal block; an elongate electrically conductive link being provided having a first end electrically connected to, or comprising, one of the terminals and extending to bridge, whilst being electrically insulated from, an end portion of the one or more heating elements of the outer heating zone electrically connected to another terminal, the link being profiled such that a second end thereof is located within the tunnel and electrically connected to an end portion of the one or more heating elements of the inner heating zone.
The heating element or elements of the outer heating zone may be substantially absent from an area occupied by the tunnel.
The electrically conductive link may be of substantially rigid form and may be arranged to bridge, in spaced relationship with, the end portion of the one or more heating elements of the outer heating zone.
The tunnel may have a lower side edge profiled to accommodate entry of the link into the tunnel and also may provide secure location for the link. For this purpose the lower side edge of the tunnel may be notched, apertured, rebated or grooved.
The link may be substantially secured in the longitudinal and/or lateral direction of the tunnel by the profiled lower side edge of the tunnel.
The second end of the link may be provided with means for securing it to the base of thermal insulation material, which means may comprise a spike or pin. Such spike or pin may be integral with, or separate from, the second end of the link.
The link may be profiled such that it has a first upwardly-directed portion in the region of (at or near) the first end thereof, a second laterally-directed portion crossing over the end portion of the one or more heating elements of the outer heating zone, a third portion downwardly directed towards the base and a fourth portion laterally directed into the tunnel at the second end of the link. Additionally, the second end of the link may be directed downwardly towards the base.
The second end of the link may be welded to the end portion of the one or more heating elements of the inner heating zone.
The link may comprise metal and may be of strip form.
Another end portion of the one or more heating elements of the inner heating zone may be electrically connected to a different terminal in the terminal block from that terminal electrically connected to, or comprising, the link.
The tunnel may be provided with a laterally-extending portion proximate the peripheral wall and adapted to shield such other end portion of the one or more heating elements of the inner heating zone. Such other end portion of the one or more heating elements of the inner heating zone may be electrically connected to the same terminal in the terminal block as the bridged end portion of the one or more heating elements of the outer heating zone.
The tunnel and/or the peripheral wall and/or the dividing wall may comprise bound vermiculite.
The tunnel may be integral with the dividing wall and/or the peripheral wall.
The base may comprise microporous thermal and electrical insulation material.
The heating elements may be of ribbon form and may be supported edgewise on the base.
The electrically conductive link in the present invention which is, in effect, mechanically coupled to the tunnel, provides reliable crossing of a heating element without risk of contact therewith. Risk of movement of the link in service is minimised as a result of its securing at the tunnel at one end and at the terminal block at the other end.
For a better understanding of the invention and to show more clearly how it may be carried into effect, reference will now be made by way of example to the accompanying drawings in which: